How to create Datum B and C using opposing faces for each, both having MMC(B) cond.

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  • How to create Datum B and C using opposing faces for each, both having MMC(B) cond.

    I have many parts that require that the secondary datum B is made of two opposing faces that are perpendicular to datum A within 0.010 at MMC and the tertiary datum C is the same except its faces are perpendicular to datun A and B and is positioned within 0.010 at MMC to datum A and datum B. Like a box with extra features attached to it. The extra features would all be located to datum A, B at MMC, C at MMC whether it be positioning or profile. All holes positioned from 0.000 to 0.010 at MMC and surfaces in general within 0.016 profile tolerance.

    How is it possible to create datum B and C so they will be correctly located to A and A,B respectively with the bonus from MMC and will allow the proper bonus for all other features located to them? I looked at creating 4 planes on the faces first then constructing a square slot using those 4 planes and using it to create the datum B and C but I can not dimension datum B and C to A and A,B respectively with MMC. It'd be nice if this was more automatic.

    In the past, we have overlooked these parts or programmed the CMM incorrectly?

    Bruce

  • #2
    What if you did a plane to plane measurement? (I know that's usually a no no, but perpendicularity is a call out that will help to protect you from false data) For both B and C, make those distances into Generic circles and only capture the axis' that each datum would originally be used to capture. You would gain the ability of MMC on both features and still be originally measuring them correctly. Report your widths based on the planes to planes and use the generic's to satisfy your alignment needs.

    Good luck and watch out for workplane errors.

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    • #3
      can we see the print? White out any proprietary info.
      sigpicSummer Time. Gotta Love it!

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